Method for completing oil wells



Nov. 4, 1941. l. s. sALNlKov 2,261,292

METHOD FOR COMPLETING OIL WELLS Filed July 25, 1959 Qua/n IN1/ENTOR.

y BY

ATTORNEY.

Patented Nov. I4, 1941 METIOD FOR COMPLETIN G WELLS Ivan S. Salnikov, Tulsa, O kla., assignor to Stand'- ard Oil Development Company, a corporation of Delaware Application July 25, 1939, serial N0. 286,311

(ci. 16s-2 1) 17 Claims.

The present invention is directed to a method for completing wells which traverse a plurality. of producing horizons and has for its particular object a completion procedure which will enable the operator to produce from various horizons simultaneously. i

It has previously been the practice in the completion of wells traversing a plurality of producing horizons to set casing in the usual manner to a point adjacent the'top of the lowest producing horizonand to then perforate the casing at points adjacent the upper producing horizons. This procedure has not been entirely satisfactory for various reasons. Inthe rst place, very little of the available surface of the upper producing horizon traversed by the bore hole is made available by perforation. Moreover, this surface-of the upper producing horizon is not exposed for treatment for increasing production, such as underreaming, acid treating, andthe like. Again, thel perforations may not be properly placed which would lead to a non-uniform production of the upper horizon. l v y Accordlngto the present invention, the difliculties encountered with the previous method are eliminated by including in the string` of casing which is set, one or more sections, as may be necessary, arranged so as to be opposite the upper producing horizons, and composed of a metal or a material which can be readily removed chemically. For example, the material may be an aluminum alloy, which, is soluble in acids or strong alkalies, or a magnesium alloy which is readily soluble in acid. Again, it may be an acid or alkali soluble resin.

The present invention will be more clearly understood from the following detailed description of the accompanying drawing in which the single igure is a vertical section through a well in the process of completion in accordance with the present invention.

Referring to the drawing in detail, numeral I designates a bore hole in which is set a string of casing 2 of the conventional steel type. The bore hole traverses an upper producing horizon 3 and a lower producing horizon 4 which may be apart a distance ranging from several feet to several hundred feet.

Included in the string of casing 2 is a section 5 of material which can be eaten away by chemical action. This section is of a length correspond' ing to the thickness of substratum 3, and may, of course, be composed of one or more individual sections. As previously indicated, this section may be composed of aluminum or magnesium alloys. A suitable aluminum alloy is one containing about 1% of silicon, about 1% of magnesium, and about 0.3% of chromium, the remainder being aluminum. A suitable magnesium alloy is one containing about 3.5% aluminum, about 0.2% of manganese, about 0.3% of zinc, about 0.5% silicon, traces of copper and nickel,y and the remainder being magnesium. It will be understood, of course, that these particular compositions are given merely by way of illustration. As between the magnesium alloys and the aluminum alloys, the former are preferred for use in accordance with the present invention for several reasons. First of all, they can be welded to steel. Secondly, they are much more rapidly dissolved in acid which contains inhibitors to protect the steel casing and tubing. Finally, they are lighter for the same strength.

' In the drawing, the casing has just been set in` cement 6, and the usual cement retaining plug 1 is in place. casing just below the removable section 5. 'I'his vpacker 8 is of the type conventionally employed in the performance of cement squeeze jobs and is known as a cementretainer, and is made of a drillable material. A similar packer 9 is set in the casing above the removable section Sand ls provided with la central passage through which passes an outer tube I0 in which is arranged a tube ll of smaller diameter. 'I'he outer tube I0 terminates Just below packer 9 while the inner tube Il extends down to a point adjacent packer 8. y

With the parts in' the-position shown, a chemical is introduced through pipe I I for the purpose Aof dissolving away section 5. When section 5 is a magnesium alloy of the type referred to above, l

the corroding agent can be, hydrochloric acid having a strength in excess of about ve per cent, suitably between 10% and 35% and preferably between 15% and 30%. This acid will contain an inhibitor of the type known to the art to protect the steel tubing from corrosion. Fresh acid is forced in continuously, but at a slow enough rate to permit the acid to have its fullest effect upon the metal. lAs an indication of the rate that must be established, it may be mentionedz that with a section three feet long and three inches in internal diameter `composed of the magnesium alloy referred to above, and with 27% hydrochloric acid, the thickness of the section was reduced IAS of an inch per hour with a feed rate of acid of three gallons per hour. It will, of course, be understood that with the larger sections customarily employed in the completion ci A packer 8 is shown arranged in the wells. the feed rate of acid will be somewhat higher.

The chemical treatment is continued until the section is completely eaten away or is reduced to such a thinness that it can be readily scraped away. With a constant feed of acid into the section the completion of the chemical treatment can be determined by a decreased rate of flow of the spent acid. Another method to deter- -mine when the job is completed is to analyze the spent acid for magnesium or aluminum, as the case may be. As a practical matter, however, experience will indicate how much time is necessary for suicient removal of section 5 so that the operation can be conducted on a time basis without the necessity of resorting to a chemical analysis.

After section 5 has been dissolved out, the packers 8 and 9 and the plug 1 are drilled out as is the cement below plug 1. Then an underreaming bit is introduced into the casing and the cement behind section 5 is reamed out ,as is the cement below the casing, so that horizons 3 and 4 are exposed and the well is ready for production after the usual setting of screen.

In some cases, the producing horizons are close enough together so as to make it economical to arrange cement plug 'I just below horizon 3 instead of just above horizon 4. When this is done, the need for cement retainer 8 is eliminated.

It may be mentioned here that when the acid is properly inhibited, the section to he eaten away need not be packed oi. In this case only one tube is necessary, since the spent acid passes upwardly through the casing. It is also to be understood that the type of acid employed will be the one best suited to the corrodible material. In some instances, oxidizing acids, such as nitric acid, are preferred. Again, the practice of this invention'is not restricted to the aluminum and magnesium alloys, but may be practiced with other alloys, such as brass, and even with nonmetallic corrodible materials.

'Ihe nature and objects of the present invention having been thus described and illustrated, what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. In the completion of a well traversing a producing horizon the steps which comprise setting casing in the well to a point below said horizon, including in said casing a 'section composed of a material of necessary strength soluble in a chemical and arranged opposite said horizon, cementing the casing in place, treating said section of soluble material with a chemical capable of dissolving the same, and completing the well in the usual manner.

2. In the completion of a well traversing a plurality of producing horizons for production from an upper horizon the steps which comprise setting casing in the well to a point below said upper horizon, including in said casing a section composed of a material of necessary strength soluble in a chemical and arranged opposite said upper horizon, forcing cement behind the casing to a point above said upper horizon, treating said section of soluble material with a chemical capable of dissolving the same and then reaming out essary strength soluble in a chemical and arranged opposite said upper horizons, cementing the casing in place, treating the upper sections of soluble material with a. chemical capable of dissolving the same, and completing the well in the usual manner.

4. In the completion of a well traversing a plurality of producing horizons for production from an upper horizon the steps which comprise setting casing in the well to a point adjacent the lowermost horizon, including in said casing opposite each upper horizon a section 'composed of a material of necessary strength soluble in a chemical, forcing cement behind said casing to a point above the uppermost producing horizon, treating said sections of soluble material with a chemical capable of dissolving the same and reaming out the cement behind the sections so removed to expose said upper horizons for production.

5. A method according to claim l in which the soluble material is an aluminum alloy.

6. A method according to claim l in which the soluble material is a magnesium alloy.

'7. .A method according to claim l in which the soluble material is a magnesium alloy and the chemical employed is dilute hydrochloric acid.

8. A method according to claim 2 in which the soluble material is an aluminum alloy.

9. A method according to claim 2 in which the soluble material is a magnesium alloy.

10. A method according to claim 2 in which the soluble material is a magnesium alloy and the chemical employed is dilute hydrochloric acid.

11. In the completion of a `well traversing a producing horizon the steps which comprise setting casing in the well to a point below said horizon, including in said casing opposite said horizon a section composed of a material of necessary strength soluble in a chemical, forcing cement into said casing and behind the same. setting a cement plug in said casing below said horizon, setting a packer of drillable material in said casing above said horizon, whereby the section of casing opposite said horizon is sealed olf from the remainder of the casing, 'establishing fluid circulation between said sealed-off section and the surface, and introducing into vsaid sealed-ofi' section a chemical capable of dissolving said soluble material.

12. In the completion of a well traversing a plurality of producing horizons from an upper horizon, the steps which comprise setting casing in the well to a point below said upper horizon, including in said casing opposite said upper horizon a section composed of a material of necessary strength soluble in a chemical, forcing cement into said casing and up behind it to a point above said upper horizon, setting drillable packers in said casing on either side of the section of said soluble material, thereby sealing off said section from the remainder of the casing, establishing iluid circulation between said sealed-off section and the surface, circulating a chemical capable of dissolving said material through' said section until said material is substantially removed, drilling through said drillcement behind said section to expose said upper able packers and rearning out the cement behind said soluble material to expose said upper producing horizon.

l13. In a method of constructing a deep well having a bore penetrating a plurality of strata including a productive stratum, the steps which consist in lowering into the bore a metal pipe comprising a section readily soluble in a chemwith the soluble metal section, said chemical so# Y lution being capable of dissolving the soluble metal section without materially dissolving the insoluble metal section.

14. In a method of constructing a deep well having a bore penetrating a plurality of strata including a productive stratum, the steps which.

lution being capable of dissolving the soluble metal section without materially dissolving the iron andsteel pipe, and thereafter removing 'the cementing material' from the face of the producing stratum.

15. The method of operating awell havingl .when desired by dissolving said member by means of a chemical solution which will dissolve said member without detrimentally affecting the consist in lowering into the bore an iron or steel cient to seal the annular space above the level of v the readily soluble metal section, allowing thecement to set, introducing into the well bore a chemical solution so as to bring it into contact ferrous metal structure.

16. A method according to claim 15 in which the removable section is made of a magnesium alloy.

17. 'A method according to claim 15\ in which the removable. section is made of a magnesium alloy, and the chemical used for the removal of the sam'e is hydrochloric acid containing an inhibitor.

IVAN S. SALNIKOV. 

